What you likely did not know is that there are a number of conspiracy theories as to why 440 Hz was chosen.
Actually, it was a FB friend posting the conspiracy crap that led me to investigate. Fascinating subject. Google “Rothschild family weaponizes music.”
It appears that, over the past few centuries, the tones that have made up western classical music have fluctuated considerably. Initially, there was no standardized pitch for instruments to tune themselves to, which meant that each orchestra would be tuning to a different pitch from one another.
Ever since the 18th century, A4—the A above middle C—has been the measurement and tuning standard for western music. Depending on what part of the world the orchestra is from, however, A4 could range from anywhere between 400 Hz and 480 Hz.
Named after Heinrich Hertz, who had successfully proven the existence of electromagnetic waves in 1830, the unit of “Hz” measures a cycle per second. Famous composers like Mozart, Bach, and Beethoven all tuned their orchestras to a different pitch, and even when the tuning fork was invented, the note it produced differed depending on whose tuning fork was used.
After several attempts at remedying the difference in tuning standards between different orchestras—A435, A451, A439—the International Organization for Standardization set an international standardized pitch of 440 Hz for A4.
This isn’t universally accepted among all orchestras. For example, The New York Philharmonic uses 442 Hz, the Boston Symphony Orchestra uses 441 Hz, and many symphonies in parts of Europe use 443 Hz or 444 Hz.
Some singers prefer 432 Hz because it’s easier to hit the high notes (which is why Verdi had his orchestras tune to 432), but most string players prefer 442 Hz because it sounds “brighter.” Probably the biggest reason for 432 Hz is that it's the so-called “scientific tuning." With a just temperament (relative to A), the frequency of every A, D, and E comes out to an integer (but if you’re doing an equal temperament, then the way to get all your Cs as integers is to set C4 at 256 Hz, so A4 becomes ~430.5 Hz). Some folks think there's magic in whole numbers, and maybe it's easier to visualize harmonic ratios when they're expressed in integers. Who would have thunk?
Nikola Tesla said, “If you wish to understand the Universe think of energy, frequency and vibration.” We are all tuning forks of a kind.